Technical Field
The present invention relates to a laser device, particularly relates to the laser device including a light condensing optical system which receives a plurality of light fluxes emitted from a plurality of surface-emitting lasers through a lens array and condenses the light on an optical fiber.
Description of Related Art
Recently, a device using a high output laser is widely known in laser beam machining and laser plug art. In addition, it is well known to use not a single but a plurality of synthesized laser beam for obtaining a high-output laser light source.
For example, Patent Document 1, JP2002-202442A, discloses a multiplexing laser light source which includes a plurality of semiconductor lasers, a multi-mode optical fiber, and a light condensing optical system that condenses laser beam emitted from the plurality of semiconductor laser and coupling the condensed laser beams to the multi-mode optical fiber. The plurality of semiconductor lasers are disposed so that their light-emitting points are arranged in a row in a first direction parallel to their active layers; and said light-collecting optics system comprises a plurality of collimator lenses, each having a first aperture diameter in said first direction and a second aperture diameter larger than said first aperture diameter in a second direction perpendicular to said first direction, and provided so that they correspond to each of said plurality of said semiconductor lasers, and a collective lens for collecting said plurality of laser beams collimated by said plurality of collimator lenses and then converging the collimated laser beams on an end face of said multi-mode optical fiber.
Patent Document 2, JP2003-158332A discloses a laser diode array which includes a plurality of multi cavity laser diode tips disposed and fixed in a line to have a plurality of emission points, wherein the multi cavity laser diode tips is arranged and fixed in a row in a same direction with an array direction of an emission point of each multi cavity laser diode tips.
In addition, Patent Document 3, JP10-284779A discloses a light condenser apparatus which includes:
a light source that emits a parallel light flux having a rectangle sectional surface;
a first reflecting unit that is arranged on an optical path of the parallel light flux to reflect a part of the parallel light flux in a first predetermined angle;
a second reflecting unit that is arranged on an optical path of the light flux reflected by the first reflecting unit to reflect the light flux reflected by the first reflecting unit;
a third reflecting unit that is arranged on the optical path of the parallel light flux to reflect a part of the light flux that is not reflected by the first reflecting unit in a second predetermined angle;
a fourth reflecting unit that is arranged on an optical path of the light flux reflected by the third reflecting unit to reflect the light flux reflected by the third reflecting unit; and
a light condenser unit that condenses the light flux reflected by the second and fourth reflecting units and the light flux that is not reflected by the first and third reflecting units all at once,
wherein the second and fourth reflecting units is configured to reflect each light flux reflected by the first and third reflecting units in a parallel direction to and adjacently to the light flux that is not reflected by the first and third reflecting units.
Recently, such a device disclosed in Patent Document 4, JP2002-026452A, is well known as a high-output laser device including a surface-emitting laser array of a laser light source.
Since a surface-emitting semiconductor laser light source (to be specific, Vertical-cavity surface-emitting laser (VCSEL)) can concentrate its emission points, compared with that in an Edge-emitting LD, a large amount of light can be obtained by arranging many emission points.
In addition, it is required to collimate the light emitted from each emission point in the VCSEL by a micro lens array because such a light is a diverging light flux.
However, since the emission point in the VCSEL has an area upon surface emission, the light collimated by the micro lens necessarily becomes a slightly divergent light flux.
It is generally known in laser synthesizing to use a condenser lens with incidence on the optical fiber, and it is required to use the micro lens corresponding to each emission point. When the emission points are concentrated to have intervals of about several tens of μm in order to obtain a large amount of light, it is required to arrange each lens to have an extremely strong refractive power to include a lens surface corresponding to each emission point. Herein, the curvature radius of the lens is approximately equal to the emission-point intervals for separating the light flux.
However, when the micro lens having such an extremely strong refractive power is disposed shortly after the emission point, a magnification ratio of an entire optical system becomes high. Thereby, a light condensing diameter is caused to increase.
As a function of the laser device, it is required to condense the high-output laser to the optical fiber having a small core diameter.
When the VCSEL is concentrated by decreasing the emission-point interval, a large amount of light can be obtained. However, neither patent nor non-patent documents can disclose a solution to a problem of increase in the light condensing diameter.
Generally, when using the condenser lens with a short focal length, a spot diameter of a light beam condensed on an incident end surface of the fiber decreases. When using the lens with the short focal length, an incidence angle (angle capable of entering into the optical fiber) increases. However, it is not necessarily appropriate to arrange the focal length as short as possible since an angle of light introduced in the optical fiber (fiber NA) is also given. A light condensing optical system including the VCSEL for condensing light in the angle capable of entering into the fiber NA and for condensing light into the smaller spot diameter is not disclosed in any patent or non-patent document.